March 1, 2024

Research team takes a fundamental step towards a functional quantum internet

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A quantum repeater jump requires two sources of entangled photon pairs separated by distance L. (infinity symbols in bottom inset). One photon from each pair is sent to a central measurement node (central shaded area in the figure), where they are stored in quantum memories. Its partner photons are sent in opposite directions, also stored in quantum memories separated by a 2L distance. A measurement that quantifies the indistinguishability of the two photons arriving at the central node, similar to what was demonstrated by Figueroa’s team, can be used to entangle distant photons. Credit: Chase Wallace, Stony Brook University

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A quantum repeater jump requires two sources of entangled photon pairs separated by distance L. (infinity symbols in bottom inset). One photon from each pair is sent to a central measurement node (central shaded area in the figure), where they are stored in quantum memories. Its partner photons are sent in opposite directions, also stored in quantum memories separated by a 2L distance. A measurement that quantifies the indistinguishability of the two photons arriving at the central node, similar to what was demonstrated by Figueroa’s team, can be used to entangle distant photons. Credit: Chase Wallace, Stony Brook University

Research into quantum computing and quantum networks is taking place around the world in hopes of developing a quantum Internet in the future. A quantum Internet would be a network of quantum computers, sensors and communication devices that will create, process and transmit quantum and entangled states and is expected to improve society’s Internet system and provide certain services and securities that the current Internet does not have.

A team of Stony Brook University physicists and their collaborators have taken a significant step toward building a quantum internet testbed by demonstrating a fundamental quantum network measurement that employs quantum memories at room temperature. Their findings are described in a paper published in npj Quantum Information.

The field of quantum information essentially combines aspects of physics, mathematics, and classical computing to use quantum mechanics to solve complex problems much faster than classical computing and to transmit information in a tamper-proof manner.

Although the vision of a quantum Internet system is growing and the field has seen a surge in interest from researchers and the general public, accompanied by a sharp increase in invested capital, an actual quantum Internet prototype has not been built.

According to the Stony Brook research team, the main obstacle to achieving the potential of making communications networks more secure, measurement systems more accurate, and algorithms for certain scientific analyzes more powerful depends on developing systems capable of transmitting quantum information and entanglement through many nodes. and over long distances. These systems are called quantum repeaters and are one of the most complex challenges in current physics research.

Researchers have developed advanced quantum repeater capabilities in their latest experiments. They built and characterized quantum memories that operate at room temperature and demonstrated that these memories have identical performance, an essential feature when the goal is to build large-scale quantum repeater networks that will comprise several of these memories.

They tested how identical these memories are in their functionality by sending identical quantum states to each of the memories and performing a process called Hong-Ou-Mandel Interference on the memories’ outputs, a standard test for quantifying the indistinguishability of photon properties.

They demonstrated that the process of storing and retrieving optical qubits in their room-temperature quantum memories does not significantly distort the joint interference process and enables memory-assisted entanglement switching, a protocol for distributing entanglement over long distances and the key to build operational quantum systems. repeaters.

“We believe this is an extraordinary step toward developing viable quantum repeaters and the quantum Internet,” says lead author Eden Figueroa, Ph.D., Stony Brook Presidential Endowed Professor of Innovation and director of the Processing Center. Distributed Quantum, which holds a joint appointment at the U.S. Department of Energy’s Brookhaven National Laboratory.

Furthermore, the quantum hardware developed by the team operates at room temperature, significantly reducing the cost of operation and making the system much faster. Much of quantum research does not occur at room temperature, but at temperatures close to absolute zero, which are more expensive, slower and more technically challenging for the network. Thus, room temperature technology is promising for building large-scale quantum networks.

The team not only obtained results on quantum memory and communication at room temperature, but also patented their approach. They have received US patents on room temperature quantum storage and high repetition rate quantum repeaters.

“Making these fleets of quantum memories work together at a quantum level and in a room temperature state is essential for any quantum Internet at any scale. To our knowledge, this feat has not been demonstrated before, and we look forward to building on this research “, emphasizes Figueroa, noting that their patented technology allows them to further test the quantum network.

Co-authors Sonali Gera, a postdoctoral researcher, and Chase Wallace, a doctoral student, both in the Department of Physics and Astronomy, worked closely with Figueroa, along with other colleagues, during experimentation that, in some ways, effectively aims to “amplify” entanglement across distances, an essential function of a quantum repeater.

“As memories are capable of storing photons with a user-defined storage time, we were also able to show temporal synchronization of photon retrieval, despite photons arriving at memories at random times, which is another feature necessary to operate a quantum system. repeater system”, explains Gera.

She and Wallace add that some of the next steps in the team’s research are to build and characterize entanglement sources compatible with quantum memories and to design mechanisms to “announce” the presence of photons stored in many quantum memories.

More information:
Sonali Gera et al, Hong-Ou-Mandel Interference of Single Photon Level Pulses Stored in Independent Quantum Memories at Room Temperature, npj Quantum Information (2024). DOI: 10.1038/s41534-024-00803-2

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